As the development of image-processing techniques, the image output machines such as printers, copiers, image scanners and multifunctional machines have become more and more popular. Various automatic paper-feeding mechanisms for quickly and steadily feeding paper sheets one by one are thus developed for use with the image output machines to facilitate the image output operations. As understood, the most annoying situation occurring in an automatic paper-feeding device is probably that no paper or more than one sheet of paper is picked in a single feeding operation. It may result in idle feeding or paper stocking problem. Generally, the above situations result from the imbalance between paper pickup and paper release operations. Therefore, it is important to provide an automatic paper-feeding device that has well-controlled paper-feeding mechanism.
Please refer to FIG. 1. A conventional automatic paper-feeding device used in an image processor is schematically shown. In the paper-feeding device, a one-way clutch mechanism is employed. The one-way clutch mechanism is implemented with a shaft 11, a clockwise torsional clutch 121, a counterclockwise torsional clutch 122, a paper-pickup arm 13 and a paper-delivering roller set 14. The paper-delivering roller set 14 includes a first roller 141, a gear set 143 and a second roller 142. The first and second rollers 141 and 142 rest on the paper sheets (not shown) to be fed in a feeding mode. When the first roller 141 is transmitted by and rotates with the shaft 11, the second roller 142 is synchronously transmitted to rotate in the same direction as the first roller 141 via the gear set 143. Then, the rotating first and second rollers 141 and 142 will transmit the paper sheet in contact therewith to move on the condition that the friction force between the rollers 141 and 142 and paper is great enough to inhibit from idle rotation of the rollers. The friction force, on the other hand, should not be so great as to pick up more than one paper sheet at the same time. After the topmost paper sheet is picked up and fed, the paper-delivering roller set 14 is switched from the feeding mode in contact with the topmost paper sheet to a release mode separate from that paper sheet. Meanwhile, the paper-delivering roller set 14 is moved back to pick up and feed next topmost paper sheet.
The aforementioned purposes can be achieved by the clockwise torsional clutch 121 and the counterclockwise torsional clutch 122. The clockwise and counterclockwise torsional clutches 121 and 122, which are implemented with springs, are sleeved on the shaft 11. The clockwise torsional clutch 121 has a fixed end 124 fixed on the shaft 11 and the counterclockwise torsional clutch 122 having a fixed end 125 securely coupled to the paper delivering roller set 14. Between the clockwise torsional clutch 121 and the counterclockwise torsional clutch 122, a coupling member 123 is arranged to couple the above elements to the paper-pickup arm 13. Assuming that the rotation direction of the shaft 11 and the rollers 141 and 142 in the feeding mode is the clockwise direction, the shaft 11 and the rollers 141 and 142 rotate in the counterclockwise direction in the release mode.
When the shaft 11 rotates in the counterclockwise direction, the counterclockwise torsional clutch 122, due to the pulling effect of the fixed end 125, becomes tight on the shaft 11 so as to synchronously move with the shaft 11. Meanwhile, the paper delivering roller set 14 securely coupled to the fixed end 125 of the counterclockwise torsional clutch 122 is transmitted to synchronously rotate with the counterclockwise rotation of the shaft 11 as a whole. The paper delivering roller set 14 thus rotates back to feed next paper sheet.
For feeding a next paper sheet, the shaft 11 is switched to rotate clockwise. Meanwhile, the counterclockwise torsional clutch 122 is released and the clockwise torsional clutch 121 becomes tightened around the shaft 11 because of the pulling force of the fixed end 124 onto the shaft 11. The clamp effect of the clockwise torsional clutch 121 on the shaft 11 transmit the entire the paper delivering roller set 14 to rotate clockwise wit the shaft 11 until the paper delivering roller set 14 sustains against the paper sheets. When the paper delivering roller set 14 has rested on the topmost paper sheet and the shaft 11 keeps rotating clockwise, the paper delivering roller set 14 can not rotate further. Therefore, the continuous clockwise rotation of the shaft 11 overcomes the frictional force between the shaft 11 and the clockwise torsional clutch 121 so as to transmit the rollers 141 and 142 to rotate synchronously, thereby feeding next paper sheet.
The aforementioned paper-pickup mechanism, although capable of achieving the paper picking and feeding purposes, is disadvantageous in manufacturing and maintenance cost and laboring. For example, at least two torsional springs are required to implement the above mechanism. In addition, since the torsion adjustment is the key point for switching the feeding mode and release mode, the control of the torsion-state change is very critical. In other words, the clockwise and counterclockwise torsional clutches 121 and 122 have to be finely manufactured and precisely controlled. Once the long-term or improper use of the springs serving as the clockwise and counterclockwise torsional clutches 121 and 122 result in elastic fatigue or any other damage, the repairing or replacing work of the springs is costly.